1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing system, an image processing method, and a recording medium.
2. Description of the Related Art
Data including multiple images obtained by imaging multiple pages sequentially with a digital camera or the like while turning the pages of a book may be used. In such a case, the luminance of an image obtained by imaging a page of the book may become uneven, i.e., luminance unevenness may occur due to the unevenness of light illuminated on the page of the book, the curvature of the page in such a state that the book is open, and the like. Since the unevenness of shade partially occurs or characters in bright portions blur in the image having uneven luminance, the image may be difficult to see.
For example, Japanese Patent Application Laid-Open Publication No. 2005-269451 (hereinafter called Patent Document 1) discloses a technique for correcting the luminance unevenness of an original document image obtained by imaging the original document. In general, the correction for removing luminance unevenness to make the luminance of an image uniform is also called shading correction.
An image processing apparatus disclosed in Patent Document 1 checks a value of the luminance of each pixel in each block obtained by dividing the original document image, acquires, for each block, a luminance value corresponding to the sheet of the original document, and determines a shading correction value of each block based on the luminance value. Then, based on the determined shading correction value, shading correction is made to pixels in each block. The luminance unevenness of multiple images seems to be corrected by applying the technique disclosed in Patent Document 1 to the multiple images obtained by imaging multiple pages of a book, respectively.
However, in order to correct the luminance unevenness of the multiple images corresponding to the multiple pages of the book, respectively, using the image processing apparatus disclosed in Patent Document 1, a series of processes as mentioned above need to be performed on each image. This may increase the processing load on the image processing apparatus.
Such a problem that the processing load for correcting the luminance unevenness of multiple images increases is not limited to the case of imaging multiple pages while a book is open, and this may also happen in a case of imaging multiple pages while a file with documents and the like bound together is open.